1. Field of the Invention
The present invention relates to a piston pump for delivering hydraulic fluid, particularly for use in vehicle brake systems.
2. Description of the Prior Art
There are numerous designs of piston pumps for delivering hydraulic fluid known from the prior art. In vehicle brake systems, radial piston pumps are frequently used, which have a number of pump elements driven by means of a cam element. The known pump elements have an inlet valve and an outlet valve. The inlet valve has a spring-loaded ball that is pressed against a valve seat. Thanks to the spring loading, the inlet valve remains closed during the pressure-generating pumping action of the piston. The outlet valve also has a spring-loaded ball that is lifted away from its valve seat as soon as the pressure in a piston chamber is greater than the force of the outlet valve spring. During the intake phase, however, a vacuum is generated in the piston chamber so that the spring force closes the outlet valve, the inlet valve is lifted away from its valve seat, and hydraulic fluid is drawn into the piston chamber from an intake line. As soon as the piston has passed bottom dead center again, the compression phase begins again, in which the inlet valve is closed and pressure is built up in the piston chamber. This control by means of the spring-loaded valves results in imprecisions, particularly in the intake phase, which have a negative impact on efficiency.
In addition, the known piston pumps have an intake path extending through the piston, i.e. the piston contains a longitudinal bore and a lateral bore through which the intake of the hydraulic fluid occurs. The inlet valve is situated in a valve cage at one end of the piston. For this reason, the piston pumps according to the prior art are relatively complex and expensive to manufacture, particularly with regard to the piston bores and assembly.